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Unread 09-09-2007, 09:15 AM   #1
IAJack
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Will a bad 02 sensor not always throw a code?

Does a 02 sensor have to throw a code to be bad or can it be way out of spec without sending one?

I can only find one on my 2K TJ. It is in front of the cat on the passenger side to the side of the tranny, are there others or is this one the one that would affect fuel mileage?

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Unread 09-09-2007, 10:20 AM   #2
jgorm
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The O2 sensor can be +-25% before throwing a code. The precat O2 is the one used for fueling.
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Unread 09-09-2007, 10:41 AM   #3
Ford4Now
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What makes you think that it is bad? Just out of curiosity....
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Unread 09-09-2007, 10:52 AM   #4
IAJack
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My gas mileage has taken a steep dive? It isn't for sure yet as I have only just done a partial mileage calculation. Might be some crappy gas or whatever. I filled up the other day and only went 56 miles and my gas gauge went to 3/4 of a tank already. Could just be the gauge too as they are probably not all that accurate?
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Unread 09-09-2007, 11:49 AM   #5
Sparty
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Quote:
Originally Posted by IAJack
My gas mileage has taken a steep dive? It isn't for sure yet as I have only just done a partial mileage calculation. Might be some crappy gas or whatever. I filled up the other day and only went 56 miles and my gas gauge went to 3/4 of a tank already. Could just be the gauge too as they are probably not all that accurate?
when's the last time you've changed your plugs?
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Unread 09-09-2007, 01:00 PM   #6
nisainmi
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I just bought a 2000 a few weeks ago and had a similar problem. Only one key came with it and I wanted a spare. What I found out is this when it comes to the chipped keys.
1. You need two keys to self program, these can be purchased at e-bay and can include the programming proceedure.
2. If you do not have two keys, you will have to go to the dealer with the vin number to get started.
3. You might want to call the dealer and ask about the charge to program the new keys (purchased from e-bay or wherever) vs. buying the keys from them and then having them doing the program.
4. Like mentioned above, keep three keys incase you loose one.
Good luck and let us all know how it goes for.
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Unread 09-09-2007, 02:48 PM   #7
IAJack
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Changed the plugs last spring. I keep it as tuned as possible. I also run all synthetic fluids in it. Just turned over to 95K miles.
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Unread 09-09-2007, 03:33 PM   #8
Ford4Now
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I am having horrible gas mileage as well. Almost unbearable...thats why I asked. I do have 32" tires but I seem to only get 12-13 mpg. I just got the Jeep within the last few months and didn't expect it to be this bad so I was wondering if something was wrong with mine as well. I changed the plugs, wires, cap, rotor, air filter, and ran fuel injector cleaner through it and still no improvement. Is it worth it to to try changing the o2 sensors?
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Unread 09-09-2007, 04:08 PM   #9
IAJack
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I was averaging around 15-20 mpg depending. Usually more towards the higher end.

I have my 31" tires at 31psi too.
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Unread 09-09-2007, 05:08 PM   #10
olonam1016
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I get the same on my jeep. I'm one of those guys that pumps gas until it's to the fullest. It takes a while but after it stop for the first time, you could squeeze another 2 gallons. It's just time consuming. You'll see the full gauge wont move until you get 40 to 45 miles. I could get about 280 miles. My jeep has 3" BDS and 33 inch tires. My O2 sensor might be going bad as well to, this week i Could only get 230 miles.
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Unread 09-09-2007, 06:13 PM   #11
Stamos
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Yes, the 02 sensor can be bad and NOT throw a code. Recently I was having an issue with my 98 where it would bog, hesitate and miss at about 2500 to 4000 rpm . I changed plus, new cap, cleaned TB and checked reference on the TPS with zero results. While my throttle response was stellar, the issue was still there.

On a lark I unplugged the front 02 sensor and boom, issue solved. Obviously it threw a CEL once it was unplugged, but the rough run issue was solved. New 02 sensor and it's back to running great. It may have been that the 02 sensor wasn't outside the parameters enough to throw a CEL but bad enough to cause the issue.

Hope this helps.
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